1. Field of the Invention
The present invention relates to the registration of semiconductor wafers undergoing metrology and/or etching processes and, more particularly, to an apparatus that provides consistent registration of semiconductor wafers in order to correlate thinning and etching processes with metrology process data.
2. Description of the Prior Art
The process of measuring the thickness of an outer material layer of a semiconductor wafer is known as wafer surface metrology. During such a metrology process, a semiconductor wafer is mechanically registered to a platform of a thickness measuring instrument. This instrument generates a map that indicates an outer layer thickness over an entire surface of the wafer. The outer layer thickness map generated from this metrology process is often used in other processes that thin or etch the measured outer layer of the wafer to a desired thickness or in a desired location, respectively. These outer layer thinning and etching processes both include some type of tool that is directed onto the surface of the wafer. This tool must be properly positioned along the wafer surface to ensure that the thinning or etching process is performed at the correct location on the wafer surface. To ensure this proper wafer registration an accurate correlation between the outer layer thickness map and the position of the wafer with respect to the thinning or etching tool is required.
The current approach for correlating outer layer thickness map data with thinning or etching instrument wafer registration begins by marking the wafer with a set of alignment fiducials during the metrology process. The wafer is then placed on a larger diameter wafer which serves as a surround. The surround is made of the same material as the wafer undergoing work to maintain a consistent reaction in the thinning and etching processes along the wafer edge. The flat of the fiducialized wafer is abutted to a flat of a registration surface of like wafer material that is taped to the surface of the surround, thereby registering the wafer in one direction. The wafer metrology fiducials are then visually aligned with a corresponding set of scribe marks on an aluminum holding plate, or platen, of the instrument. Once aligned, two additional pieces of like wafer material are abutted against the wafer and taped to the surround to maintain the wafer position. The surround is then taped to the platen and the thinning or etching process may begin.
It is easily seen that the above described correlated registration procedure is time consuming and prone to human error. It is therefore desirable to accelerate this registration procedure while eliminating the potential for human error.